thanks, thanks one and all. delay in posting, but I assure you the work is in progress:
* unplugged the power antenna power wire (I guess - you can understand how googling for this information and finding good results is a challenge).
* found blue and blue-white wires from the stereo wiring harness - they were just sitting there disconnected. if you read about this stuff enough, you figure that blue is for power. That's all I'm worrying about for now.... [reads Alpine manual] - yes "blue" is "power antenna" or "power antenna lead", "Connect this lead to the B+ terminal of your power antenna, if applicable". I note that the "antenna" has a line going to the female RCA-ish connector on the back of the Alpine head, as expected. so never mind anything besides the "blue", plain-blue wire.
... the power antenna wire thin wire (If you do this, you'll know what that means) was plugged into something. Not sure where it goes. Will have to reach further. for now both connectors are disconnected. looks like I need an adequate gauge of power wire - I guess copper, I guess 18 gauge - and a typical spade connector but on the other end, I need some sort of more narrow connector to match the original antenna power wire.
there's other curiosities in there, but focusing on the known knowns for now. This sounds like I'm making a mountain out of a molehill but it ought to at least cover the topic for any poor audio-ignorant soul out there... Will report back.
pics below (not necessarily in order):
